What can I get done to achieve a "crease" under my butt cheeks?

Buttock crease depends on your anatomy. If you do not have it already, some plastic surgeons can help. We create this with buttock contouring with liposuction and fat transfer. Make sure you see a "real" plastic
surgeon. Do your homework well before the consult.

   This will depend upon your current anatomy.  This area can be sculpted with a combination of liposuction and fat grafting to create a cuff.  This is not easy so find a surgeon who has done it hundreds of times.Kenneth Hughes, MDLos Angeles, CA

Every patient has a different buttock shape, some have a long crease under the buttocks, in others the crease is short and some others there is no crease. For an evaluation of your case, it is important to see some photos of the buttock area and see what needs to be done to crease a crease. It can be by adding fat just above the crease, or removing some fat under the buttocks, also can be done by adding some fat toward the middle of the lower pole of the buttocks.

Hello dear!!
Thanks for the question and provided information as well.
Unfortunately, without pictures, it is very difficult to give you a proper answer.
In general, you need to be physically healthy and at a stable weight, have realistic expectations, be a non-smoker and your BMI needs to be 30 or less. l recommend you to make an appointment with a board certified plastic surgeon to talk about your goals and anything you need to know.
Good luck :)

This is something that talented plastic surgeons are able to achieve with this procedure. Consult with a board-certified plastic surgeon to determine whether this is a plausible outcome for you and whether your PS is experienced in this specific work.

It is unclear based on your description alone as to whether you need more fat injected above the infragluteal fold or whether a lower buttock lift/tuck would be more beneficial. You would have to provided pictures for a more specific answer

The crease of cuff is
achieved during the procedure by techniques of liposuction and fat transfer.
You should consult your plastic surgeon that did the procedure about the same.